In the following excerpt, Barnes discusses Democritus's skepticism regarding humankind's ability to know anything with certainty.

Democritean Scepticism

Metrodorus of Chios, a pupil of Democritus (e.g., Clement, 70 A 1) who held solidly to the main tenets of atomism (e.g., Theophrastus, A 3), purveys an extreme scepticism which foreshadows, in its ingenious comprehensiveness, the most extravagant claims of Pyrrho: at the beginning of his book Concerning Nature Metrodorus said:

None of us knows anything, not even that very fact whether we know or do not know; nor do we know what not to know and to know are, nor, in general, whether anything is or is not.

(505: B 1)1

Of Metrodorus' book little else survives and nothing tells us what his scepticism rested upon, or why he wrote Concerning Nature at all...